公元前510年，罗马共和国在意大利半岛崛起，其最重要的国家机构是（   ）

如图，在平面直角坐标系中，二次函数y=x²+bx+c的图象与x轴交于A、B两点，A点在原点的左则，B点的坐标为(3，0)，与y轴交于C(0，-3)点，点P是直线BC下方的抛物线上一动点。

⑴求这个二次函数的表达式；
⑵连结PO、PC，在同一平面内把△POC沿CO翻折，得到四边形POP′C，那么是否存在点P，使四边形POP′C为菱形？若存在，请求出此时点P的坐标；若不存在，请说明理由；
⑶当点P运动到什么位置时，四边形ABPC的面积最大，并求出此时P点的坐标和四边形ABPC的最大面积．

下列四个图示中，能正确表示染色体、DNA，基因三者在概念上的大小关系的是（　　）

阅读下面短文，从短文后所给的A、B、C三个选项中选出能填入相应空白处的最佳选项。

    What is the best way to study? This is a very important question. Some Chinese students often 1 very hard for long hours. This is a 2 habit, but it is not a better way to study. An efficient (高效的) student must 3 enough sleep, enough food and enough rest. Every week you 4 to go out for a walk or visit some friends or some nice places. It's good for your study. When you 5back to your study, you'll find yourself 6 than before and you'll learn more.

    Maybe we can 7that learning English is like taking Chinese medicine. We don't mean that it's 8. We mean that like Chinese medicine, the effect (效果) of your study 9 slowly but surely.

     10 slowly but surely every day and effects will come just like Chinese medicine.